Many products currently marketed and sold to consumers are designed for limited use. These products are usually associated with a single event, a restricted time period or restricted access. There are many reasons for the need of single use or limited use products.
An example of a single use product is a disposable syringe. Instrument contamination and cross infection between patients is an ever present concern if the syringe is inadvertently reused. It is a particular concern in some countries where repeated use of instruments is known to transmit serious diseases such as HIV and hepatitis. Medical and ophthalmic devices that must be sterilized such as scalpels or tonometers (for the measurement of a patient's intraocular pressure) body piercing and tattooing instruments used on multiple clients also give cause for concern. Needles used in acupuncture offer another example. Decontamination procedures or employment of single-use devices are methods used to control cross infection, but they rely on personnel awareness, willingness to follow protocol, monitoring and documentation.
The limited use type of product is usually associated with goods that should be used for a restricted time period. One example of this type of product is “daily wear” or disposable contact lenses. Contact lenses for refractive correction or cosmetic purposes require suitable wear and care regimes in order to maintain good eye health. Non-compliance on the part of the patient, either through choice or due to lack of education, can injure the eye. Frequent replacement lenses are sometimes worn for longer than recommended or they may be stored or cleaned inappropriately.
A number of patents have tried to address the requirements for single use, limited use, or restricted access products.
U.S. Pat. No. 3,899,295 describes the use of an indicator containing a pH sensitive dye applied to the container of a product such as a medical instrument. The indicator displays a first color in a normal atmosphere, then following introduction of a basic atmosphere the sensor displays a second color. The problem with this patent is that the indicator is not displaying information relating to the condition of the product contained within the package. Since the indicator is not incorporated within or fixed onto the product, the information given actually relates to the container, not its contents. An additional problem with this patent is that the basic atmosphere in which the product is stored is chlorine gas which is highly reactive to the materials that comprise many of the products that one could imagine being supplied in a sterile package container, such as metal surgical instruments and many pharmaceutical compounds or drugs.
Similarly, U.S. Pat. No. 4,098,577 by the same inventor describes a similar pH sensitive indicator and two different atmospheric conditions, however that invention describes the indicator change in the presence of an acidic atmosphere. As described above, the indicator is not incorporated within or fixed onto the product, therefore the information presented by the indicator relates to the container, not its contents.
U.S. Pat. No. 4,526,752 presents a tamper resistant package with an indicator means. The invention describes a container which incorporates an indicator within its structure to display information on whether a container has been previously opened. As with other patents, the indicator relates to the condition of the package and not the product contained in the package.
U.S. Pat. No. 6,790,411 describes a solution based hydrogen peroxide indicator where the solution has a first color in normal atmospheric conditions, then following a sterilization process using hydrogen peroxide, the solution exhibits a second color. One will certainly recognize a problem with this technique by considering the case where a package that has been sterilized with hydrogen peroxide, is subsequently tampered with, punctured, or otherwise damaged and made non sterile, while the indicator still displays the sterile condition.
U.S. Pat. No. 6,851,808 describes an ophthalmic lens product with an attached indication means that provides the user information relating to the products condition or previous use. The invention overcomes many of the problems with the previously described patents. However, since the indicator means described in the patent uses changes in the product's light environment as the initiator for the use indication display, and since variations exist in the lighting environment where the product is used, the use indication can present at a rate that is faster or slower than that which is optimally desired.